题解 | #判断链表中是否有环#

//golang. 哈希方法和双指针
package main

import . "nc_tools"

/*
 * type ListNode struct{
 *   Val int
 *   Next *ListNode
 * }
 */

/**
 *
 * @param head ListNode类
 * @return bool布尔型
 */
 /*
func hasCycle(head *ListNode) bool {
	// write code here
	traveled := make(map[*ListNode]bool)
	for head != nil {
		if traveled[head] {
			return true
		}
		traveled[head] = true
		head = head.Next
	}
	return false
}
*/

func hasCycle(head *ListNode) bool {
	// write code here
	if head == nil || head.Next == nil {
		return false
	}
	slow, fast := head, head.Next
	for slow != fast {
		if fast == nil || fast.Next == nil {
			return false
		}
		slow = slow.Next
		fast = fast.Next.Next
	}
	return true
}